Webster's English Dictionary

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thunder

1. thun.der \'th*n-d*r\ n [ME thoner, thunder, fr. OE thunor; akin to OHG 
   thonar]thunder, L tonare to thunder 1a: the sound that follows a flash of 
   lightning and is caused by sudden exp ansion of the air in the path of the 
   electrical discharge archaic  1b: a discharge of lightning : THUNDERBOLT  
   2: a loud utterance or threat  3: BANG, RUMBLE 
2. thunder \-d(*-)rin\ \-d*r-*r\ vb or thun.der.ing 1a: to produce thunder 
   - usu. used impersonally {it ~ed}  1b: to give forth a sound likened to 
   thunder {horses ~ed dow n the road} 2: ROAR, SHOUT  1: to utter loudly : 
   ROAR  2: to strike with a sound likened to thunder  - thun.der.er n